Exploring the association between dietary Inflammatory Index and chronic pain in US adults using NHANES 1999–2004

Chronic pain, a substantial public health issue, may be influenced by dietary patterns through systemic inflammation. This cross-sectional study explored the association between Dietary Inflammatory Index (DII) and chronic pain among 2581 American adults from NHANES data. The DII, ranging from − 4.98 to 4.69, reflects the inflammatory potential of the diet, with higher scores indicating greater pro-inflammatory capacity. Our findings showed no significant association between the continuous DII score and chronic pain prevalence. However, a nonlinear relationship emerged. When the DII was categorized, a significant association between higher DII scores (DII ≥ 2.5) and chronic pain prevalence was observed. The analysis uncovered a U-shaped pattern, with an inflection point at a DII score of − 0.9, indicating an association between both low and high levels of dietary inflammation are associated with higher pain prevalence. This nuanced interaction between dietary inflammation and chronic pain indicates the possibility of incorporating dietary modification into pain management strategies and underscores the need for further research into the long-term effects of diet on chronic pain.

a Less than 500 kcal or more than 5000 kcal is considered as excessively energy intake.
All analyses have been weighted to account for the survey's complex sampling design.
Model I: Adjusted for age and sex.
Model II: Adjusted for age, sex, race, marital status, poverty income ratio, and education level.
Model III: Adjusted for all these variables, including age, sex race, marital status, poverty income ratio, education level, body mass index, physical activity, smoking status, coronary heart disease, stroke, dietary supplements taken, hypertension, diabetes mellitus and C-reactive protein.

Figure S1
. Weighted analysis of the interaction between dietary inflammatory index and chronic pain.
Abbreviations: BMI: body mass index; CI: confidence interval; OR: odd ratio; Note: P for interaction represents the likelihood of interaction between the variable and dietary inflammatory index.
Each stratified factor was analyzed for its interaction with the dietary inflammatory index on chronic pain, adjusting for all other variables, including age, sex, marital status, race/ethnicity, education level, household income, smoking status, physical activity, hypertension, diabetes, stroke, coronary heart disease, body mass index, energy expenditure, protein consumption, carbohydrate consumption, fat consumption, dietary supplements taken, and C-reactive protein, with the exception of the stratification variable itself.

Figure S2.
Non-linear association between the dietary inflammatory index and chronic pain in individuals who do not have excessively energy intake.
Note: The curve presented in the figure is based on a weighted restricted cubic spline model to illustrate the non-linear association between the dietary inflammatory index and chronic pain in individuals who do not have excessively energy intake.Adjusted for age, sex, race, marital, poverty income ratio, education level, body mass index, physical activity, smoking status, coronary heart disease, stroke, hypertension, diabetes mellitus, dietary supplements, and C-reactive protein levels.

Introduction
Background / rationale #2 Explain the scientific background and rationale for the investigation being reported 3-5 Objectives #3 State specific objectives, including any prespecified hypotheses 5

Study design #4
Present key elements of study design early in the paper 5-6 Setting #5 Describe the setting, locations, and relevant dates, including periods of recruitment, exposure, follow-up, and data collection

5-6
Eligibility criteria #6a Give the eligibility criteria, and the sources and methods of selection of participants.6

Table S1 .
Comparison of basic characteristics between excluded and included populations (age ≥ 20).

Table S2 .
Nutrient intake according to the quartiles of the DII

Table S3 .
The relationship between DII and chronic pain in individuals who do not have excessively energy intake a CI, confidence interval; DII: dietary inflammatory index; OR, odd ratio; Ref: reference.
Report numbers of individuals at each stage of study-eg numbers potentially eligible, examined for eligibility, confirmed eligible, included in the study, completing follow-up, and analysed.Give information separately for for exposed and unexposed groups if applicable.Discuss limitations of the study, taking into account sources of potential bias or imprecision.Discuss both direction and magnitude of any potential bias.Give a cautious overall interpretation considering objectives, limitations, multiplicity of analyses, results from similar studies, and other relevant evidence.Give the source of funding and the role of the funders for the present study and, if applicable, for the original study on which the present article is based 22 None The STROBE checklist is distributed under the terms of the Creative Commons Attribution License CC-BY.This checklist can be completed online using https://www.goodreports.org/,a tool made by the EQUATOR Network in collaboration with Penelope.ai